Abstract
BackgroundCoat protein complex I (COPI) vesicles, coated by seven coatomer subunits, are mainly responsible for Golgi-to-ER transport. Silkworm posterior silkgland (PSG), a highly differentiated secretory tissue, secretes fibroin for silk production, but many physiological processes in the PSG cells await further investigation.Methodology/Principal FindingsHere, to investigate the role of silkworm COPI, we cloned six silkworm COPI subunits (α,β,β′, δ, ε, and ζ-COP), determined their peak expression in day 2 in fifth-instar PSG, and visualized the localization of COPI, as a coat complex, with cis-Golgi. By dsRNA injection into silkworm larvae, we suppressed the expression of α-, β′- and γ-COP, and demonstrated that COPI subunits were required for PSG tube expansion. Knockdown of α-COP disrupted the integrity of Golgi apparatus and led to a narrower glandular lumen of the PSG, suggesting that silkworm COPI is essential for PSG tube expansion.Conclusions/SignificanceThe initial characterization reveals the essential roles of silkworm COPI in PSG. Although silkworm COPI resembles the previously characterized coatomers in other organisms, some surprising findings require further investigation. Therefore, our results suggest the silkworm as a model for studying intracellular transport, and would facilitate the establishment of silkworm PSG as an efficient bioreactor.
Highlights
The silkworm, Bombyx mori, produces silk, and is considered as one of the best-characterized biological model organisms [1,2]
We found that complex I (COPI) deficiency disrupts the Golgi apparatus and causes narrower posterior silkgland (PSG) glandular lumen, indicating that COPI is essential for the integrity of endomembrane system in PSG cells and for PSG tube expansion
We demonstrated that the absence of silkworm COPI led to tube expansion deficiency of the PSG, and further established that COPI deficiency disrupts the integrity of the Golgi apparatus
Summary
The silkworm, Bombyx mori, produces silk, and is considered as one of the best-characterized biological model organisms [1,2]. One of the major silk components, is composed of heavy chain proteins, light chain proteins, and P25, and is secreted by the posterior silkgland (PSG) [3,4]. The fibroincontaining vesicles are potentially transported by BmKinesin-1 from the Golgi apparatus to the apical cytoplasm, and the fibroin is released into the glandular lumen [5]. PSG cells devote 85% of their protein synthesis to silk production [8]. It is necessary to understand the molecular mechanisms of various intracellular transport processes in PSG, including fibroin secretion, which are still largely elusive. Silkworm posterior silkgland (PSG), a highly differentiated secretory tissue, secretes fibroin for silk production, but many physiological processes in the PSG cells await further investigation
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